Processing Reliability

Storm provides two types of guarantees when processing tuples for a Storm topology.

Table 1. Processing Guarantees
Guarantee	Description
At least once	Reliable; Tuples are processed at least once, but may be processed more than once. Use when subsecond latency is required and for unordered idempotent operations.
Exactly once	Reliable; Tuples are processed only once. (This feature requires the use of a Trident spout and the Trident API.